A skeleton from a Mexican cave is one of the oldest humans ever discovered in North America. Andrew Masterson reports.

A prehistoric human skeleton in the Chan Hol cave near Tulúm on the Yucatán peninsula, prior to looting by unknown cave divers.

Tom Poole, Liquid Junge Lab

Radioactive dating of skeletal remains unearthed in a Mexican cave indicates the area was settled by humans at least 13,000 years ago.

Research conducted by a team led by Wolfgang Stinnesbeck of Heidelberg University in Germany set out to resolve contradictory previous results obtained using carbon-14 dating by testing the location using a different technique, known as uranium-thorium dating.

This method measures the degree to which naturally occurring uranium-234 – with a half-life of 245,000 years – decays into thorium-230, with a half-life of 75,000 years. The method is accurate up to a range of half a million years

Although the now-established age of the bones is well within the dating range of the carbon-14 method, earlier tests had delivered wildly varying estimates. This, the researchers explain, is because over thousands of years the cave has been repeatedly inundated with both salt and fresh water – leaching almost all the collagen, which is essential for carbon dating, from the bones and teeth.

Rather than attempt to date the skeletal remains themselves, the researchers instead dated a stalactite growing a few milimetres above the pelvis, and a rock deposit known as a speleotherm nearby.

The results gave a date range of approximately 11,000 to 13,000 years, with Stinnesbeck considering the latter to be more likely.

This suggests that the Chan Hol remains comprise one of the oldest humans ever discovered in North America.